1. Field of the Invention
This invention relates to a drum brake device suitable for a heavy-duty commercial vehicle.
2. Description of Related Art
A cylinder device in combination of a hydraulic operated type service brake and a mechanical wedge operated type parking brake is disclosed in the Published Unexamined Japanese Utility Model Application Number 57-141241.
A conventional cylinder device a is explained with reference to FIGS. 8 and 9, where a cylinder body b is configured with three pistons Cl-C3 slidably fitting therein in series.
The cylinder body b is comprised of a first boss b1 through which a rod d of a wedge-actuating mechanism is penetrated and a second boss b2 having inlet and outlet ports for a brake fluid. A fitting portion, which includes both boss b1 and boss b2, is fitted into a fitting hole g opened in a back plate e and a reinforcing plate f superposed thereon to be fixed by bolts n.
When in service-brake operation, the brake fluid is supplied to a hydraulic chamber i formed between the piston c2 and the piston c3 via a brake pipe j in order to separate a pair of brake shoes k, k. While in parking brake operation, the pair of brake shoes k, k separate by pulling a wedge inserted between the intermediate piston c2 and a piston c1 via rollers.
In the above-conventional structure, the pair of brake shoes k, k tend to accidentally tilt because an opening side of the brake drum (not shown in the figures) deforms outward and a bending force is exerted on the back plate e and the reinforcing plate f via an anchor which is supporting the brake shoes k, k. A biasing force affecting the cylinder body b during this condition is supported by the back plate e and the reinforcing plate f.
The above-described conventional drum brake device suffers from the following drawbacks that need improvement.
The fitting portion including the first boss b1 and the second boss b2 of the cylinder device a is fit in the fitting hole g provided in the back plate e and the reinforcing plate f. For the purpose of reducing the total weight of the drum brake device, in order to avoid enlarging the thick reinforcing plate f, the distance between the first boss b1 and the second boss b2 is designed to be shorter. Therefore, the conventional device has disadvantage in connecting the brake pipe j on the second boss b2 and in air bleeding work by loosening a bleeder (not shown in figure) mounted on the member m of the second boss b2. Further, the conventional device leaves a possibility of damaging a dust boot h during the above-described operation.
In order to resolve the above-described problem, if the fitting hole g is enlarged to lengthen the distance between the first boss b1 and the second boss b2, the thickness of the reinforcing plate f and back plate e must be increased or an outside form of the reinforcing plate f must be enlarged to provide reinforcement; thereby, causing another problem of the weight increase and the difficulty in the design layout.
It is an object of this invention to provide a cylinder device for a drum brake device which improves workability in connecting the brake pipe and in bleeding the air as well as enables to lightening the drum brake device.
This invention is a torque-receiving member and a brake cylinder arrangement for a drum brake device. The brake cylinder has a plurality of pistons slidably housed in series within a cylinder body. A wedge-actuating mechanism comprises a wedge and rollers positioned between one pair of two facing pistons among said plurality of pistons. A hydraulic chamber is formed between the other pair of two facing pistons among said plurality of pistons, and cylinder body is fixed on said torque-receiving member. A first boss is formed in the cylinder body through which a rod of the wedge-actuating mechanism is penetrated. A second boss positioned away from the first boss of the cylinder body has an inlet port and an outlet port for a fluid channel leading to the hydraulic chamber. The first boss is fit into a boss-fitting hole of the torque-receiving member, and the second boss is positioned adjacent to the outside of the outermost end of the torque-receiving member.
This invention further is a torque receiving member and a brake cylinder arrangement for a drum brake device, wherein fluid channels, leading from the inlet port and outlet port to the hydraulic chamber, consist of a slope channel running from the inclined end surface of said second boss toward hydraulic chamber and a straight channel running from the flat surface of second boss to an intermediate portion of slope channel. The fluid channel is a combination of the slope channel and the straight channel is a xe2x80x9c less than xe2x80x9d shape, and an opening of the slope channel is closed airtight.
This invention still further is a torque-receiving member and a brake cylinder arrangement for a drum brake device, wherein the opening of the slope channel is closed airtight by a plug. A top of said plug is positioned adjacent to a cross-point portion between slope channel and the straight channel so as to minimize the residual space of slope channel.
This invention still further is a torque-receiving member and a brake cylinder arrangement for a drum brake device, wherein the wedge-actuating mechanism is configured to push a rod to apply the brake.
This invention yet is a torque-receiving member and a brake cylinder arrangement for a drum brake device, wherein the wedge-actuating mechanism is configured to pull said rod to apply the brake.